1. Field of the Invention
The present invention relates to vehicle speed display apparatus. More particularly, the invention relates to a vehicle speed display apparatus for a vehicle which can be switched between 2WD and 4WD, in which an accurate readout of vehicle speed may be obtained in either 2WD mode or in 4WD mode.
2. Description of the Background Art
Japanese patent publication no. JP-UM-B-1-22093 discloses a vehicle speed display unit in which the number of pulses proportional to the rotational speed of the wheel is counted per unit of travel distance, and the counted value is input into a calculating circuit for calculating and displaying the vehicle speed. The number of pulses per unit travel distance is proportional to the rotational speed of the wheel.
The traveling speed of the vehicle is, as is disclosed in the publication described above, normally obtained by detecting the number of pulses proportional to the rotational speed of the wheel, and calculating and outputting the detected number of pulses.
There is a known 4-wheeled buggy (ATV: All Terrain Vehicle), the driving mode of which can be switched between 2WD and 4WD for usages as a traveling vehicle for agriculture or cattle breeding and as a recreational vehicle. In such a four-wheeled buggy, a difference between the rotational speed of the front wheel and the rotational speed of the rear wheel may be calculated in advance, to improve operability during travel. In the 4WD mode, for example, the rotational speed of the front wheel may be set in advance to a lower value than the rotational speed of the rear wheel.
Considering the use of the number of pulses that is proportional to the rotational speed of the wheel for displaying the vehicle speed of the four-wheeled buggy, as is disclosed in the aforementioned publication, since the rotational speed between the driving wheel (rear wheel) and the driven wheel (front wheel) are substantially the same when traveling in the 2WD mode, it is possible to display a value which matches the actual vehicle speed by obtaining the vehicle speed from the relation between the detected number of pulses and the actual vehicle speed and displaying the obtained value.
However, when a difference between the rotational speed of the front wheel and the rotational speed of the rear wheel in the 4WD mode is calculated in advance, as described above, the relation between the detected number of pulses and the actual vehicle speed is different from 2WD mode. In 4WD mode, the speed obtained and displayed in the same manner as in the 2WD mode has a margin of error with respect to the actual vehicle speed, and thus the displayed value is not the actual exact vehicle speed.
In view of such circumstances, it is an object of the present invention to provide a vehicle speed display apparatus for a vehicle which can be switched between 2WD and 4WD, in which an accurate display of the actual vehicle speed may be obtained in either 2WD mode or 4WD mode.
Although the known devices have some utility for their intended purposes, there is still a need to provide an improved vehicle speed display apparatus for an all-terrain vehicle, which is capable of accurately displaying vehicle speed in either 2WD or in 4WD. In particular, there is a need for an improved vehicle speed display apparatus including components designed to solve the above-mentioned problems.